1. Field of the Invention
The invention relates to a solar power generation system which interconnects with an alternating current power system.
2. Description of the Related Art
In general, an inverter is used in a solar power generation system to interconnect with an alternating current (AC) power system. The inverter converts a direct current (DC) power generated by a solar cell into an AC power which synchronizes with the AC power system, to supply the power to the AC power system. Moreover, on an AC output side of the inverter, an overcurrent relay is disposed to protect the inverter.
However, the overcurrent relay for use in this way performs the following false operation sometimes. When a system voltage drops owing to a fault or the like of the AC power system, an amplitude of a ripple of an alternating current output from the inverter increases. In consequence, even when an instantaneous value of a current of a fundamental component is not in excess of a setting value at which the overcurrent relay operates, the instantaneous value due to the amplitude of the ripple of the current exceeds the setting value, so that the overcurrent relay operates sometimes. In this case, the overcurrent relay is to bring about a false operation.